1. Field of the Invention
The invention relates to an electricity meter which has sigma delta modulators and a digital signal processing device.
German Published, Non-Prosecuted Patent Application DE 40 21 522 A1, corresponding to U.S. Pat. No. 4,943,888, has disclosed an electronic switch which includes a sigma delta modulator (.SIGMA..DELTA. modulator) for each network phase to be detected and in which the modulator is followed by a decimation filter. Outputs of the decimation filter are connected to one another through a switching logic having an output that is fed to an actuator for breaking the current supply. The switch serves to detect an excess of current and to switch off at a predetermined limit value. When there is a malfunction inside one of the signal channels, e.g. an interruption, it is possible that an excess current will not be detected so that it is also not possible for a triggering to occur.
Published European Patent Application 0 634 662 A1 has disclosed an electricity meter which has signal channels with multiplexers having inputs that are connected to current signals and voltage signals of a consumer, that are detected by converter. Furthermore, sigma delta modulators and a digital signal processing device are provided therein.